Previous research has indicated that many older adults tend to have serious deficits in spatial (pattern) vision, despite the fact that they are considered to be in good ocular health. Although the field has made great strides in describing these disorders, we are still unclear as to what factors, both optical and neural, underlie this aging-related decline in older adults' spatial sensitivity. The proposed studies are designed to continue our research elucidating these underlying mechanisms, using non- invasive, psychophysical (behavioral) measurement techniques. As in our earlier work, we will be focusing on spatial vision in older adults who are free from identifiable ocular disease. We recognize, however, that there is a fine line between what is called "normal" biological aging vs. specific disease processes that tend to occur in the elderly. Yet it is necessary to understand impairments in visual function that can occur in later life even in those individuals considered to be in good ocular health. Experiments will examine three specific questions: (1) To what extent are optical changes in the aged eye responsible or spatial contrast sensitivity losses in older adults? (2) To what extent are changes in the spatial tuning of neural mechanisms underlying spatial vision responsible for decreases in spatio-temporal sensitivity in later life? (3) The third question we will address involves patients with intraocular lenses (IOLs), today the most common treatment for elderly patients after cataract extraction. We will examine how differences in the modulation transfer function of the IOL vs. the normal aged crystalline lens relates to spatial contrast sensitivity differences in these patients. The long-term objective of this research is to achieve a better understanding of the optical and neural factors underlying older adults' deficits in spatial vision, so that improved treatments and solutions can be developed to minimize and eliminate these visual deficits.